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Mapping quantitative trait loci (QTL) in sheep. II. Meta-assembly and identification of novel QTL for milk production traits in sheep

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15 pages
An (Awassi × Merino) × Merino backcross family of 172 ewes was used to map quantitative trait loci (QTL) for different milk production traits on a framework map of 200 loci across all autosomes. From five previously proposed mathematical models describing lactation curves, the Wood model was considered the most appropriate due to its simplicity and its ability to determine ovine lactation curve characteristics. Derived milk traits for milk, fat, protein and lactose yield, as well as percentage composition and somatic cell score were used for single and two-QTL approaches using maximum likelihood estimation and regression analysis. A total of 15 significant ( P < 0.01) and additional 25 suggestive ( P < 0.05) QTL were detected across both single QTL methods and all traits. In preparation of a meta-analysis, all QTL results were compared with a meta-assembly of QTL for milk production traits in dairy ewes from various public domain sources and can be found on the ReproGen ovine gbrowser http://crcidp.vetsci.usyd.edu.au/cgi-bin/gbrowse/oaries_genome/ . Many of the QTL for milk production traits have been reported on chromosomes 1, 3, 6, 16 and 20. Those on chromosomes 3 and 20 are in strong agreement with the results reported here. In addition, novel QTL were found on chromosomes 7, 8, 9, 14, 22 and 24. In a cross-species comparison, we extended the meta-assembly by comparing QTL regions of sheep and cattle, which provided strong evidence for synteny conservation of QTL regions for milk, fat, protein and somatic cell score data between cattle and sheep.
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Genetics Selection Evolution
BioMedCentral
Open Access Research Mapping quantitative trait loci (QTL) in sheep. II. Meta-assembly and identification of novel QTL for milk production traits in sheep Herman W Raadsma*, Elisabeth Jonas, David McGill, Matthew Hobbs, Mary K Lam and Peter C Thomson
Address: ReproGen  Animal Bioscience Group, Faculty of Veterinary Science, University of Sydney, 425 Werombi Road, Camden NSW 2570, Australia Email: Herman W Raadsma*  raadsma@camden.usyd.edu.au; Elisabeth Jonas  ejonas@camden.usyd.edu.au; David McGill  dmcgill@csu.edu.au; Matthew Hobbs  matthew.hobbs@usyd.edu.au; Mary K Lam  maryl@mail.usyd.edu.au; Peter C Thomson  petert@camden.usyd.edu.au * Corresponding author
Published: 22 October 2009Received: 2 July 2009 Accepted: 22 October 2009 Genetics Selection Evolution2009,41:45 doi:10.1186/1297-9686-41-45 This article is available from: http://www.gsejournal.org/content/41/1/45 © 2009 Raadsma et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract An (Awassi × Merino) × Merino backcross family of 172 ewes was used to map quantitative trait loci (QTL) for different milk production traits on a framework map of 200 loci across all autosomes. From five previously proposed mathematical models describing lactation curves, the Wood model was considered the most appropriate due to its simplicity and its ability to determine ovine lactation curve characteristics. Derived milk traits for milk, fat, protein and lactose yield, as well as percentage composition and somatic cell score were used for single and two-QTL approaches using maximum likelihood estimation and regression analysis. A total of 15 significant (P< 0.01) and additional 25 suggestive (P< 0.05) QTL were detected across both single QTL methods and all traits. In preparation of a meta-analysis, all QTL results were compared with a meta-assembly of QTL for milk production traits in dairy ewes from various public domain sources and can be found on the ReproGen ovine gbrowser http://crcidp.vetsci.usyd.edu.au/cgi-bin/ gbrowse/oaries_genome/. Many of the QTL for milk production traits have been reported on chromosomes 1, 3, 6, 16 and 20. Those on chromosomes 3 and 20 are in strong agreement with the results reported here. In addition, novel QTL were found on chromosomes 7, 8, 9, 14, 22 and 24. In a cross-species comparison, we extended the meta-assembly by comparing QTL regions of sheep and cattle, which provided strong evidence for synteny conservation of QTL regions for milk, fat, protein and somatic cell score data between cattle and sheep.
Background Sheep represent an economically important agricultural resource in the global meat, fibre, and milk production systems of both the developed and developing world. The multipurpose nature of many sheep breeds and the highly specialised single purpose breeds, demonstrate the versatility and suitability of sheep production in a diverse
set of production systems [1]. Sheep milk production rep resents a specialised commodity which has been devel oped across many breeding systems in either dual purpose, synthetic composite lines, or specialised dairy breeds such as the Awassi, Chios, Comisana, Lacaune, Laxta and Sarda Breeds [2]. Genetic variation has been reported for most of the major milk traits, and has been
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